The present invention relates to the use of an intermittent sequence of messages to maintain synchronisation between a transmitter and at least one receiver in a communication network. In particular, it relates to transmitters and receivers for use in such a network.
In a communication network comprising a plurality of transceivers it may be necessary to keep the transceivers synchronised so that they use the same timing for communicating between each other. One transceiver may act as a master defining the timing for the communication system with the others acting as slaves and keeping synchronised with the timing of the master. It may be desirable to keep power consumption of the slaves as low as possible.
One way of maintaining synchronisation within the network is for the master to transmit a periodic sequence of single beacon messages, with a fixed time interval between the beacon messages. A beacon message may be a radio packet. The slaves periodically listen, every fixed time interval, for a beacon message. The periodic reception of a beacon message from the master allows the slave to compare its timing with that of the master and to adjust its timing to maintain synchronisation. Furthermore, as the sequence is periodic, power consumption can be reduced if the slave receiver does not attempt to receive beacon messages in the interval between beacon messages. Consequently, the slave receivers may listen for a beacon message in a listening window of fixed duration centred at the time a beacon message is expected to be received, once every fixed time interval.
There are some problems with such a system. The system is susceptible to the loss of beacon messages. Loss may arise from interference or multipath propagation causing degradation of the beacon message such that it is not received in the listening window of the receiver. Loss may also arise if the timing of the master is varied. Such variation may be desirable when a transceiver is part of a host device such as a mobile phone which operates with a timing system which is not synchronised to the master. It may be useful to synchronise the host timing and the master timing by shifting the timing of the master so that it coincides with the host's timing.
It would be desirable to improve synchronisation within a communications network.